To a surface layer of an electrophotographic photosensitive member, a stress caused by electrophotographic processes, such as a charging process, an exposure process, a development process, a transfer process, and a cleaning process, has been repeatedly applied. Therefore, the surface layer of the electrophotographic photosensitive member has been required to have abrasion resistance and chemical stability.
Methods for increasing the abrasion resistance of the surface layer of the electrophotographic photosensitive member include a method for blending a polymerized product of a hole transporting compound (hole transportation substance) in the surface layer of the electrophotographic photosensitive member. The polymerized product of the hole transporting compound is a kind of curable resin.
However, when a high abrasion-resistant surface layer is provided, the surface layer is difficult to be abraded, so that the surface of the surface layer is difficult to be refreshed, which is likely to cause accumulation of chemical deteriorated-substances on the surface of the surface layer. The chemical deteriorated-substances mainly include those formed by a chemical change of the polymerized product of the hole transporting compound due to the repeated application of the stress by the electrophotographic processes described above.
The chemical change of the polymerized product of the hole transporting compound sometimes may cause a phenomenon in which an image (electrophotographic image) output in a high humidity environment, particularly, in a high temperature and high humidity environment becomes unclear (hereinafter also referred to as “image deletion”).
Therefore, in order to suppress the image deletion, it has been required to suppress the chemical change of the polymerized product of the hole transporting compound.
Techniques for suppressing the chemical degradation of the hole transporting compound include a technique for blending additives in the surface layer of the electrophotographic photosensitive member together with the polymerized product of the hole transporting compound.
PTL 1 discloses a technique for suppressing the image deletion by blending a specific fluorine atom containing monomer having a polymerizable functional group in a surface layer of an electrophotographic photosensitive member.
PTLs 2, 3, and 4 disclose a technique for suppressing the image deletion by blending a specific amine compound in a surface layer of an electrophotographic photosensitive member.
However, the technique using additives disclosed in each patent literature described above is a technique for reducing the stress to be applied to the polymerized product of the hole transporting compound and is not a technique for increasing the chemical stability of the hole transporting compound itself.
In recent years, an increase in the durability of the electrophotographic photosensitive member has noticeably proceeded and a technique for suppressing the image deletion has been further demanded. In order to further suppress the image deletion, it has been required to not only reduce the above-described stress but increase the chemical stability of the hole transporting compound itself.